Activatable Fluorophores for the Molecular Imaging of Cytosolic Phospholipase A2 in Breast Cancer

Breast cancer is the most commonly diagnosed cancer in women and the number two cause of cancer associated death. Surgery is the first line of defense in treating breast cancer and the success of surgery has been shown to predict the probability of cancer reoccurrence. Near Infrared (NIR) fluorescence guided surgery offers the potential to increase the accuracy of surgical resection by the use of fluorescence imaging agents targeted towards cancer. Cytosolic Phospholipase A2 (cPLA2) activity is enhanced in triple negative breast cancer and is associated with resistance to therapy in luminal-like cancers. The goal of this work is to develop activatable fluorophores targeted towards cPLA2 and evaluate their use for the molecular imaging of breast cancer in order to determine their potential as contrast agents for NIR fluorescence guided surgery. A series of tricyclic fluorophores were caged through esterification with fatty acids. Arachidonic acid was utilized to generate cPLA2 selective probes and palmitic acid was used to generate control probes. In vitro, probes were shown to activate in the presence of purified PLA2 and results were used to identify the most promising probe: DDAO arachidonate. Cellular fluorescence spectroscopy and microscopy showed DDAO arachidonate activated in breast cancer cell lines expressing cPLA2, where control probe did not. Modulation of cPLA2 activity through inhibition, induction, and genetic knockdown, resulted in corresponding changes in fluorescence generation. In a panel of breast cancer cell lines, cPLA2 expression, varied based on molecular subtype and correlated with DDAO arachidonate activation. Finally, DDAO arachidonate, when painted onto human triple negative tumor mouse xenografts, resulted in selective activation of tumor but not surrounding healthy tissue. Together, these results indicate DDAO arachidonate is a useful agent for measuring cPLA2 activity in both breast cancer cells and tumors and may offer the potential to aid in the fluorescence guided surgery of triple negative breast cancer